Energy Storage:
Keeping the lights on when the sun goes down

One objection to renewable energy is that it can be unpredictable and intermittent. People use energy 24 hours a day, but wind turbines turn only when the wind blows and solar panels don't work at night. By comparison, nuclear fission is predictable, adjustable and always available. This issue is often used as an argument to support the continued use of Nuclear power.

However, new designs for solar energy systems get around the problem by using heat stores. These capture any excess energy when it's generated, releasing it later when needed.

Heat stores

Water: At the Solucar solar power plant in Spain, mirrors shine the sun at a tower which boil water flowing through it. This resulting steam can used to spin turbines for generating electricity, or stored in large insulated tanks. This stored heat is released to run the turbines at night, when there is less demand for electricity.

Molten Salt: Water isn't the only liquid that can be used to store heat. Other solar generators have used the sun to heat already molten salt still hotter. This can be stored in insulated tanks as a liquid, and pumped at night to heat exchangers to boil water into steam which runs turbines to generate elctricity.

Compressed air stores

Wind turbines also work at night when we use much less electricity. It is possible for the spare electricity generated to be stored by using it to pump air into deep underground chambers where it builds up under pressure. During the day, the compressed air can be released to drive turbines when the electricity is needed.  more info

The future of solar power